It is well known that substantial muffling of internal combustion engines is necessary in order to reduce objectionable noise. However, it is desirable to reduce the level of exhaust noise without seriously interfering exhaust outflow. A large variety of mufflers have been developed in an attempt to meet these twin objectives for internal combustion engines.
In some environments where internal combustion engines are used, it is mandatory that the emission of glowing carbon particles from the exhaust be prevented so as to avoid fires in the surrounding environment. This is particularly true in applications such as off road motorcycles or "dirt bikes." A spark arresting muffler capable of catching and retaining sparks of carbon and the like discharged by the engine are necessary in such an environment because any sparks which might otherwise escape to the surroundings pose a fire hazard. Various arrangements have been provided for this purpose. One such design is shown in U.S. Pat. No. 3,987,867 issued on Oct. 26, 1976. Another such design is illustrated in the U.S. Pat. No. 4,113,051 patent which issued on Sep. 12, 1978. U.S. Pat. Nos. 3,987,867 and 4,113,051 are both owned by the assignee of the instant application. Both of these patents are incorporated into this specification by reference in their entireties.
The known muffler and spark arrester designs have an enclosure including a perforated inner tube which is coaxially located within an outer tube. A sound absorbent material is placed between the tubes. At the outlet end of the inner and outer tubes there is provided a gas barrier wall with a partially toroidal concave configuration. Against this wall nests a plurality of partially toroidal disks slightly spaced apart by edge dimples.
One of the problems with the conventional mufflers described in the two patents referenced above is that they employ circular disks. Unfortunately, the "disk efficiency" of circular disks decreases as their diameter increases. This is because the material required for the disk increases by the outer diameter of the disk squared but the flow area of the disk only increases in direct proportion to the disk's diameter.
Another disadvantage of the conventional mufflers illustrated in the two above-identified patents is that they are relatively large in size and do not meet today's needs for streamlined mufflers in both motorcycles and cars, as well as in other types of vehicles, such as jet skis.
Accordingly, it has been considered desirable to develop and new and improved muffler system which would overcome the foregoing difficulties and others while providing better and more advantageous overall results.